An OLED (organic light emitting diode) display is a self-luminous display. As compared to a LCD (liquid crystal display), the OLED display is lighter and thinner because the OLED display does not need a backlight source. Furthermore, the OLED display also has merits of high brightness, low power consumption, wide viewing angle, high response speed, wide operating temperature range, and so on, and thus it is more and more applied to various high-performance display fields.
The light-emitting mechanism of the OLED is that, under the action of an externally-applied electric field, electrons and holes are injected into an organic luminous material from positive and negative electrodes, respectively, and thus they migrate, recombine and decay in the organic luminous material to give off light.
For the OLED device, a relatively large number of holes will gather at a side of the organic luminous material close to an electron transportation layer in the course of light emission because mobility of a hole transportation material is far greater than mobility of an electron transportation material. Thus, this leads to imbalance of transportation between holes and electrons and other carriers, and luminance is greatly reduced.
A typical structure of a conventional OLED device may be that illustrated in FIG. 1, which comprises an anode layer 102′, a cathode layer 112′ and an organic thin film layer 13′ located between these two layers, and furthermore, diverse functional layers including an electron injection layer 1041′, an electron transportation layer 1042′, a hole injection layer 1031′, a hole transportation layer 1032′ and an organic light emitting layer 105′ may be comprised in the organic thin film layer 13′. The organic light emitting layer 105′ usually comprises organic luminous materials for three colors of red, green and blue. To keep holes, electrons and other carriers in balance during the transportation, a hole blocking layer 12′ will usually be formed between the organic light emitting layer 105′ formed of the organic luminous materials for three colors of red, green and blue and the electron transportation layer 1042′. However, the shortcoming of this structure lies in that, an OLED device with this structure needs to experience multiple patterning processes, so as to form the organic light emitting layer 105′ possessing three colors of red, green and blue and the hole blocking layer 12′, respectively. In this way, not only the fabrication process is relatively cockamamie and complex, but also requirements on accuracy of workmanship are also relatively high. Thus, yield of products is seriously restraint, and the production cost of products is raised.